Organophosphorus-treated zeolite catalysts for para-selective aromatics conversion

ABSTRACT

A method is provided for treating modified ZSM-5 type zeolite catalysts with a vapor phase organophosphorus reagent such as trimethylphosphite or dimethylmethylphosphonate in order to improve the para-selective properties of such catalysts for the conversion of aromatic materials. The modified zeolites so treated are those which contain a minor proportion of a difficultly reducible oxide such as magnesium oxide, calcium oxide and/or phosphorus oxide. Such catalyst compositions can be used in alkylation, transalkylation or disproportionation processes to provide alkylated aromatic product mixtures having exceptionally high concentrations of the para-dialkylbenzene isomer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of copending U.S. application Ser. No.489,424, filed April 28, 1983 now U.S. Pat. No. 4,469,806, which is acontinution-in-part of U.S. application Ser. No. 359,560, filed Mar. 18,1982, now U.S. Pat. No. 4,409,132. The entire disclosures of theseapplications and patents are expressly incorporated herein by reference.

BACKGROUND

The present invention relates to the preparation and use of modifiedzeolite catalyst compositions which are especially suitable for theconversion of aromatic hydrocarbons to provide product mixtures enrichedin the para-(or 1,4-) dialkyl substituted benzene isomer.

Production of dialkyl substituted benzene compounds via alkylation,transalkylation or disproportionation of aromatic hydrocarbons is animportant step in a number of commercial chemical manufacturingprocesses. Such reactions can be carried out over a variety of catalystmaterials. Alkylation of aromatic hydrocarbons utilizing crystallinealuminosilicate catalysts has, for example, been described. U.S. Pat.No. 2,904,697 to Mattox refers to alkylation of aromatic hydrocarbonswith an olefin in the presence of a crystalline metallic aluminosilicatehaving uniform openings of about 6 to 15 Angstrom units. U.S. Pat. No.3,251,897 to Wise describes alkylation of aromatic hydrocarbons in thepresence of X or Y-type crystalline aluminosilicate zeolites,specifically such type zeolites wherein the cation is rare earth and/orhydrogen. U.S..Pat. No. 3,751,504 to Keown et al. and U.S. Pat. No.3,751,506 to Burress describe vapor phase alkylation of aromatichydrocarbons with olefins, e.g., benzene with ethylene, in the presenceof a ZSM-5 type zeolite catalyst.

The disproportionation of aromatic hydrocarbons in the presence ofzeolite catalysts has been described by Grandio et al in the Oil and GasJournal, Vol. 69, No. 48 (1971), U.S. Pat. Nos. 3,126,422; 3,413,374,3,598,878; 3,598,879 and 3,607,961 show vapor-phase disproportionationof toluene over various catalysts.

In many of these prior art processes, the dialkylbenzene productproduced frequently contains more of the 1,3 isomer than of the othertwo isomers. For example, xylene produced via the conventional catalyticmethylation of toluene can have the equilibrium composition ofapproximately 24 percent of 1,4-, 54 percent of 1,3- and 22 percent of1,2- isomer. Of the dialkylbenzene isomers, 1,3-dialkylbenzene is oftenthe least desired product, with 1,2- and 1,4-dialkylbenzene being themore useful products. 1,4-Dimethylbenzene, for example, is of particularvalue, being useful in the manufacture of terephthalic acid which is anintermediate in the manufacture of synthetic fibers such as "Dacron".Furthermore, 1,4- methylethylbenzene, i.e., para-ethyltoluene (PET), isuseful for subsequent conversion to para-methylstyrene, and for thispurpose ethyltoluene products containing as much as 97% of the paraisomer can be required.

Mixtures of dialkylbenzene isomers, either alone or in further admixturewith ethylbenzene, have previously been separated by expensivesuperfractionation and multistage refrigeration steps. Such processes,as will be realized, involve high operation costs and have a limitedyield. Alternatively, various modified zeolite catalysts have beendeveloped to alkylate toluene with a greater or lesser degree ofselectivity to 1,4-dialkylbenzene isomers. Hence, U.S. Pat. Nos.3,972,832, 4,034,053, 4,128,592, and 4,137,195 disclose particularzeolite catalysts which have been treated with compounds of phosphorusand/or magnesium to increase para-selectivity of the catalysts.Para-selective boron-containing zeolites are shown in U.S. Pat. No.4,067,920 and para-selective, antimony-containing zeolites in U.S. Pat.No. 3,979,472. Similarly, U.S. Patent Nos. 3,965,208; 4,117,026;4,259,537; 4,260,843; 4,275,256; 4,276,437; 4,276,438; 4,278,827 and4,288,647 all disclose other zeolites modified with various oxides toimprove catalyst para-selectivity.

Even though catalyst treatment procedures have been developed to renderzeolite catalysts highly para-selective for aromatics conversion,aromatics conversion processes employing such catalysts, and especiallysuch processes conducted on a commercial scale, generally tend to have adeselectivating effect on the catalyst. Contaminants such as moisture,metals and/or halogen introduced into the catalyst bed with the feed orwith diluents can markedly lower catalyst para-selectivity. Water formedin the catalyst bed as a reaction product of the hydrocarbon conversionreactions which occur therein (e.g. when a methanol reactant isemployed) can also adversely affect catalyst para-selectivity. There isthus a continuing need to develop not only aromatic conversion catalystswhich have high initial para-selectivity, but also catalyst treatmentprocedures which are useful for restoring diminished catalystpara-selectivity and reducing catalyst susceptibility to subsequentdeselectivation.

Accordingly, it is an object of the present invention to provide methodsfor treating para-selective zeolite-based aromatics conversion catalyststo enhance their initial or subsequently diminished para-selectivitycharacteristics or to reduce catalyst susceptibility to subsequentdeselectivation.

It is a further object of the present invention to provide modifiedzeolite catalyst compositions which effectively promote the conversionof aromatics to produce mixtures containing an exceptionally highpercentage, e.g., 80% by weight or more for alkylation of toluene, ofpara-dialkylbenzene isomer.

It is a further object of the present invention to provide highlypara-selective aromatics conversion processes employing the modifiedzeolite catalysts described herein.

SUMMARY

The present invention provides a method for treating modified zeolitecatalysts to render such catalysts highly para-selective and resistantto deselectivation by water or halogen contaminants when used for theconversion of aromatic compounds to produce dialkyl substituted benzenecompounds. The zeolite component of the catalysts so treated is onewhich has a silica to alumina mole ratio of at least 12 and a constraintindex within the approximate range of 1 to 12. Such zeolite catalystsare further modified by incorporation thereinto of a minor proportion ofa difficultly reducible oxide.

In accordance with the present invention, such catalysts are contactedwith an organophosphorus reagent in the vapor phase at a temperaturebetween about 100° C. and 300° C. for a period of time and underconditions sufficient to either enhance catalyst para-selectivity orreduce catalyst susceptibility to deselectivation by contact withmoisture or halogen. The organophosphorus reagents employed in suchtreatment can be the C₁₋₄ alkylphosphite esters, the C₁₋₄ alkylphosphateesters, or dimethylmethylphosphonate.

The present invention also relates to modified catalyst compositionstreated in this manner and to alkylation, transalkylation anddisproportionation processes utilizing such treated modified catalystcompositions.

DETAILED DESCRIPTION

The catalysts which are treated in accordance with the method of thepresent invention are zeolite based catalysts which promote theconversion of aromatic compounds. One essential component of suchcatalysts is a particular type of crystalline zeolite material whichexhibits unusual properties. Although these zeolites have unusually lowalumina contents, i.e. high silica to alumina mole ratios, they are veryactive even when the silica to alumina mole ratio exceeds 30. Suchactivity is surprising, since catalytic activity is generally attributedto framework aluminum atoms and/or cations associated with thesealuminum atoms. These zeolites retain their crystallinity for longperiods in spite of the presence of steam at high temperature whichinduces irreversible collapse of the framework of other zeolites, e.g.of the X and A type. Furthermore, carbonaceous deposits, when formed,may be removed by burning at higher than usual temperatures to restoreactivity. These zeolites, used as catalysts, generally have lowcoke-forming activity and therefore are conducive to long times onstream between regenerations by burning carbonaceous deposits withoxygen-containing gas such as air.

An important characteristic of the crystal structure of this particularclass of zeolites is that it provides a selective constrained access toand egress from the intracrystalline free space by virtue of having aneffective pore size intermediate between the small pore Linde A and thelarge pore Linde X, i.e. the pore windows of the structure are of abouta size such as would be provided by 10-membered rings of silicon atomsinterconnected by oxygen atoms. It is to be understood, of course, thatthese rings are those formed by the regular disposition of thetetrahedra making up the anionic framework of the crystalline zeolite,the oxygen atoms themselves being bonded to the silicon or aluminumatoms at the centers of the tetrahedra. Briefly, the preferred typezeolites useful in this invention possess, in combination: a silica toalumina mole ratio of at least about 12; and a structure providingconstrained access to the intracrystalline free space.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminamole ratio of at least 12 are useful, it is preferred in some instancesto use zeolites having substantially higher silica/alumina ratios, e.g.70 and above, 200 and above or even 1600 and above. In addition,zeolites as otherwise characterized herein but which are substantiallyfree of aluminum, that is zeolites having silica to alumina mole ratiosof up to infinity, are found to be useful and even preferable in someinstances. Such "high silica" or "highly siliceous" zeolites areintended to be included within this description. Thus also to beincluded within the zeolite definition are substantially pure silicaforms of the useful zeolites described herein, that is to say thosezeolites having no measurable amount of aluminum (silica to alumina moleratio of infinity) but which otherwise embody the characteristicsdisclosed.

Members of this particular class of zeolites, after activation, acquirean intracrystalline sorption capacity for normal hexane which is greaterthan that for water, i.e. they exhibit "hydrophobic" properties. Thishydrophobic character can be used to advantage in some applications.

The zeolites of the particular class useful herein have an effectivepore size such as to freely sorb normal hexane. In addition, theirstructure must provide constrained access to larger molecules. It issometimes possible to judge from a known crystal structure whether suchconstrained access exists. For example, if the only pore windows in acrystal are formed by 8-membered rings of silicon and aluminum atoms,then access by molecules of larger cross-section than normal hexane isexcluded and the zeolite is not of the desired type. Windows of10-membered rings are preferred, although in some instances excessivepuckering of the rings or pore blockage may render these zeolitesineffective. Twelve-membered rings usually do not offer sufficientconstraint to produce the advantageous conversions, although thepuckered 12-ring structure of TMA offretite shows constrained access.Other 12-ring structures may exist which may be operative.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access to molecules oflarger cross-section than normal paraffins, a simple determination ofthe "Constraint Index" as herein defined may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a sample of zeolite at atmospheric pressureaccording to the following procedure. A sample of the zeolite, in theform of pellets or extrudate, is crushed to a particle size about thatof coarse sand and mounted in a glass tube. Prior to testing, thezeolite is treated with a stream of air at 540° C. for at least 15minutes. The zeolite is then flushed with helium and the temperature isadjusted between 290° C. and 510° C. to give an overall conversion ofbetween 10% and 60%. The mixture of hydrocarbons is passed at 1 liquidhourly space velocity (i.e., 1 volume of liquid hydrocarbon per volumeof zeolite per hour) over the zeolite with a helium dilution to give ahelium to (total) hydrocarbon mole ratio of 4:1. After 20 minutes onstream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

The "Constraint Index" is calculated as follows: ##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index of about 1 to 12.Constraint Index (CI) values for some typical materials are:

    ______________________________________                                        Zeolite             C.I.                                                      ______________________________________                                        ZSM-5               8.3                                                       ZSM-11              8.7                                                       ZSM-12              2                                                         ZSM-23              9.1                                                       ZSM-35              4.5                                                       ZSM-38              2                                                         ZSM-48              3.4                                                       TMA Offretite       3.7                                                       Clinoptilolite      3.4                                                       Catalyst-56         1.5                                                       H--Zeolon (mordenite)                                                                             0.4                                                       REY                 0.4                                                       Amorphous Silica-Alumina                                                                          0.6                                                       Erionite            38                                                        ______________________________________                                    

The above-described Constraint Index is an important and even criticaldefinition of those zeolites which are useful in the instant invention.The very nature of this parameter and the recited technique by which itis determined, however, admit of the possibility that a given zeolitecan be tested under somewhat different conditions and thereby exhibitdifferent Constraint Indices. Constraint Index seems to vary somewhatwith severity of operation (conversion) and the presence or absence ofbinders. Likewise, other variables such as crystal size of the zeolite,the presence of occluded contaminants, etc., may affect the constraintindex. Therefore, it will be appreciated that it may be possible to soselect test conditions as to establish more than one value in the rangeof 1 to 12 for the Constraint Index of a particular zeolite. Such azeolite exhibits the constrained access as herein defined and is to beregarded as having a Constraint Index in the range of 1 to 12. Alsocontemplated herein as having a Constraint Index in the range of 1 to 12and therefore within the scope of the defined class of highly siliceouszeolites are those zeolites which, when tested under two or more sets ofconditions within the above-specified ranges of temperature andconversion, produce a value of the Constraint Index slightly less than1, e.g. 0.9, or somewhat greater than 12, e.g. 14 or 15, with at leastone other value within the range of 1 to 12. Thus, it should beunderstood that the Constraint Index value as used herein is aninclusive rather than a exclusive value. That is, a crystalline zeolitewhen identified by any combination of conditions within the testingdefinition set forth herein as having a Constraint Index in the range of1 to 12 is intended to be included in the instant novel zeolitedefinition whether or not the same identical zeolite, when tested underother of the defined conditions, may give a Constraint Index valueoutside of the range of 1 to 12.

The particular class of zeolites defined herein is exemplified by ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other similarmaterials.

ZSM-5 is described in greater detail in U.S. Pat. Nos. 3,702,886 and Re.29,948. The descriptions contained within those patents include theX-ray diffraction pattern of therein disclosed ZSM-5.

ZSM-11 is described in U.S. Pat. No. 3,709,979. The description in thatpatent includes the X-ray diffraction pattern of said ZSM-11.

ZSM-12 is described in U.S. Pat. No. 3,832,449. The description in thatpatent includes the X-ray diffraction pattern for ZSM-12.

ZSM-23 is described in U.S. Pat. No. 4,076,842 along with aspecification of the X-ray diffraction pattern of the disclosed ZSM-23zeolite.

ZSM-35 is described in U.S. Pat. No. 4,016,245 along with a descriptionof the X-ray diffraction pattern of the zeolite.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. Thedescription of that zeolite in that patent includes the X-raydiffraction pattern of ZSM-38.

ZSM-48 is more particularly described in U.S. Pat. No. 4,375,573. Such adescription includes the X-ray diffraction pattern for ZSM-48.

It is to be understood that by incorporating by reference the foregoingpatent documents to describe examples of specific members of thespecified zeolite class with greater particularity, it is intended thatidentification of the therein disclosed crystalline zeolites be resolvedon the basis of their respective X-ray diffraction patterns. Asdiscussed above, the present invention contemplates utilization of suchcatalysts wherein the mole ratio of silica to alumina is essentiallyunbounded. The incorporation of the identified patent documents shouldtherefore not be construed as limiting the disclosed crystallinezeolites to those having the specific silica-alumina mole ratiosdiscussed therein, it now being known that such zeolites may besubstantially aluminum-free and yet, having the same crystal structureas the disclosed materials, may be useful or even preferred in someapplications. It is the crystal structure, as identified by the X-raydiffraction "fingerprint", which establishes the identity of thespecific crystalline zeolite material.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intra-crystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 540° C. for one hour, for example, followed by baseexchange with ammonium salts followed by calcination at 540° C. in air.The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this type zeolite; however, thepresence of these cations does appear to favor the formation of thisspecial class of zeolite. More generally, it is desirable to activatethis type catalyst by base exchange with ammonium salts followed bycalcination in air at about 540° C. for from about 15 minutes to about24 hours.

Natural zeolites may sometimes be converted to zeolite structures of theclass herein identified by various activation procedures and othertreatments such as base exchange, steaming, alumina extraction andcalcination, alone or in combinations. Natural minerals which may be sotreated include ferrierite, brewsterite, stilbite, dachiardite,epistilbite, heulandite, and clinoptilolite.

The preferred crystalline zeolites for utilization herein include ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48, with ZSM-5 beingparticularly preferred.

In a preferred aspect of this invention, the zeolites hereof areselected as those providing among other things a crystal frameworkdensity, in the dry hydrogen form, of not less than about 1.6 grams percubic centimeter. It has been found that zeolites which satisfy allthree of the discussed criteria are most desired.

Therefore, the preferred zeolites useful with respect to this inventionare those having a Constraint Index as defined above of about 1 to about12, a silica to alumina mole ratio of at least about 12 and a driedcrystal density of not less than about 1.6 grams per cubic centimeter.The dry density for known structures may be calculated from the numberof silicon plus aluminum atoms per 1000 cubic Angstroms, as given, e.g.,on Page 19 of the article Zeolite Structure by W. M. Meier. This paper,the entire contents of which are incorporated herein by reference, isincluded in Proceedings of the Conference on Molecular Sieves, (London,April 1967) published by the Society of Chemical Industry, London, 1968.

When the crystal structure is unknown, the crystal framework density maybe determined by classical pycnometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. Or, the crystaldensity may be determined by mercury porosimetry, since mercury willfill the interstices between crystals but will not penetrate theintracrystalline free space.

It is possible that the unusual sustained activity and stability of thisspecial class of zeolites is associated with its high crystal anionicframework density of not less than about 1.6 grams per cubic centimeter.This high density must necessarily be associated with a relatively smallamount of free space within the crystal, which might be expected toresult in more stable structures. This free space, however, is importantas the locus of catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                      Void     Framework                                                            Volume   Density                                                ______________________________________                                        Ferrierite      0.28   cc/cc   1.76   g/cc                                    Mordenite       .28            1.7                                            ZSM-5, -11      .29            1.79                                           ZSM-12          --             1.8                                            ZSM-23          --             2.0                                            Dachiardite     .32            1.72                                           L               .32            1.61                                           Clinoptilolite  .34            1.71                                           Laumontite      .34            1.77                                           ZSM-4 (Omega)   .38            1.65                                           Heulandite      .39            1.69                                           P               .41            1.57                                           Offretite       .40            1.55                                           Levynite        .40            1.54                                           Erionite        .35            1.51                                           Gmelinite       .44            1.46                                           Chabazite       .47            1.45                                           A               .5             1.3                                            Y               .48            1.27                                           ______________________________________                                    

When synthesized in the alkali metal form, the zeolite is convenientlyconverted to the hydrogen form, generally by intermediate formation ofthe ammonium form as a result of ammonium ion exchange and calcinationof the ammonium form to yield the hydrogen form. In addition to thehydrogen form, other forms of the zeolite can be employed as precursorsto the oxide-modified zeolites of the present invention. Such otherforms of the zeolite are those wherein the original alkali metal contenthas been reduced to less than about 50 percent by weight of the originalalkali metal contained in the zeolite as synthesized, usually 0.5percent by weight or less. Thus, the original alkali metal of thezeolite may be replaced by ion exchange with other suitable metalcations of Groups I through VIII of the Periodic Table, including, byway of example, nickel, copper, zinc, palladium, calcium or rare earthmetals.

In practicing aromatics conversion processes using the treated catalystof the present invention, it may be useful to incorporate theabove-described crystalline zeolites with a matrix comprising anothermaterial resistant to the temperature and other conditions employed insuch processes. Such matrix materials include synthetic or naturallyoccurring substances as well as inorganic materials such as clay, silicaand/or metal oxides. The latter may be either naturally occurring or inthe form of gelatinous precipitates or gels including mixtures of silicaand metal oxides. Naturally occurring clays which can be composited withthe zeolite include those of the montmorillonite and kaolin families,which families include the sub-bentonites and the kaolins commonly knownas Dixie, McNamee-Georgia and Florida clays or others in which the mainmineral constitutent is halloysite, kaolinite, dickite, nacrite oranauxite. Such clays can be used in the raw state as originally mined orinitially subjected to calcination, acid treatment or chemicalmodification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may bein the form of a cogel. The relative proportions of zeolite componentand inorganic oxide gel matrix, on an anhydrous basis, may vary widelywith the zeolite content ranging from between about 1 to about 99percent by weight and more usually in the range of about 5 to about 80percent by weight of the dry composite.

A second essential component of the aromatics conversion catalyststreated in accordance with the present invention comprises a minorproportion, e.g., from about 0.05% to 50% by weight of the catalystcomposite, of a difficultly reducible oxide, incorporated into thezeolite. Oxides of this type can include oxides of phosphorus as well asthose oxides of the metals of Groups IA, IIA, IIIA, IVA, VA, VIA, VIIA,VIIIA, IB, IIB, IIIB, IVB, or VB of the Periodic Chart of the Elements(Fisher Scientic Company, Catalog No. 5-702-10) which serve to enhancethe para-selectivity properties of the catalysts modified therewith. Thedifficultly reducible oxides most commonly employed to modify theselectivity properties of the zeolite-based catalysts herein are oxidesof phosphorus and magnesium. Thus, the catalysts herein can be treatedwith phosphorus and/or magnesium compounds in the manner described inU.S. Pat. Nos. 3,894,104; 4,049,573; 4,086,287; and 4,128,592, thedisclosures of which are incorporated herein by reference.

Phosphorus, for example, can be incorporated into such catalysts atleast in part in the form of phosphorus oxide in an amount of from about0.25% to about 25% by weight of the catalyst composition, preferablyfrom about 0.7% to about 15% by weight. Such incorporation can bereadily effected by contacting the zeolite composite with a solution ofan appropriate phosphorus compound, followed by drying and calcining toconvert phosphorus in the zeolite to its oxide form. Preferredphosphorus-containing compounds include diphenyl phosphine chloride,trimethylphosphite and phosphorus trichloride, phosphoric acid, phenylphosphine oxychloride, trimethylphosphate, diphenyl phosphinous acid,diphenyl phosphinic acid, diethylchlorothiophosphate, methyl acidphosphate and other alcohol-P₂ O₅ reaction products. Particularlypreferred are ammonium phosphates, including ammonium hydrogenphosphate, (NH₄)₂ HPO₄, and ammonium dihydrogen phosphate, NH₄ H₂ PO₄.Calcination is generally conducted in the presence of oxygen at atemperature of at least about 150° C. However, higher temperatures,i.e., up to about 500° C. or higher are preferred. Such heating isgenerally carried out for 3-5 hours but may be extended to 24 hours orlonger.

As discussed more fully hereinafter, the optional incorporation ofphosphorus into the zeolite composite as one of the useful difficultlyreducible oxides is a catalyst treatment procedure distinct from thesubsequent essential catalyst treatment step of the present inventionwhich involves contact of the catalyst composite with particular vaporphase organophosphorus reagents under particular reaction conditions. Itis thus possible for a catalyst composite to be modified in accordancewith the present invention by two separate treatments with phosphoruscompounds, the first of such treatments serving to incorporate an oxideof phosphorus as all or part of the difficultly reducible oxidecomponent and the second such treatment serving to provide theadditional catalyst para-selectivity benefits of the present invention.

Magnesium oxide is another preferred difficultly reducible oxide whichcan be incorporated with the zeolite composites in a manner similar tothat employed with phosphorus. Magnesium can comprise from about 0.25%to 25% by weight preferably from about 1% to 15% by weight present atleast in part as magnesium oxide. As with phosphorus, magnesium oxideincorporation is effected by contacting the zeolite composite with anappropriate magnesium compound followed by drying and calcining toconvert magnesium in the zeolite to its oxide form. Preferredmagnesium-containing compounds include magnesium nitrate and magnesiumacetate. Calcination times and temperatures are generally the same asrecited hereinbefore for calcination of phosphorus-containing catalysts.

In addition to treatment of the zeolite composites to incorporatephosphorus and/or magnesium oxides as hereinbefore described in detail,such zeolites may also be modified in a substantially similar manner toincorporate thereinto a variety of other oxide materials to enhancepara-selectivity. Such oxide materials include oxides of boron (U.S.Pat. No. 4,067,920); antimony (U.S. Pat. No. 3,979,472); beryllium (U.S.Pat. No. 4,260,843); Group VIIA metals (U.S. Pat. No. 4,275,256);alkaline earth metals (U.S. Pat. No. 4,288,647); Group IB metals (U.S.Pat. No. 4,276,438); Group IVB metals (U.S. Pat. No. 4,278,827); GroupVIA metals (U.S. Pat. No. 4,259,537); Group IA elements (U.S. Pat. No.4,329,533); cadmium (U.S. Ser. No. 139,611, filed Apr. 11, 1980); ironand/or cobalt (U.S. Ser. No. 150,868, filed May 19, 1980); Group IIIBmetals (U.S. Pat. No. 4,276,437); Group IVA metals (U.S. Pat. No.4,302,620); Group VA metals (U.S. Pat. No. 4,302,621); and Group IIIAelements (U.S. Pat. No. 4,302,622).

Treatment of the zeolite catalysts to incorporate any of the foregoingoxide materials to enhance para-selectivity will generally occur beforesuch catalysts are treated with organophosphorus materials in accordancewith the present invention in order to provide even greater enhancementand/or restoration of the para-selective properties of such catalysts.Additional catalyst modifying procedures which may also optionally beemployed to modify catalyst activity or selectivity include precokingand presteaming (i.e., before oxide incorporation), or combinationsthereof.

In accordance with the present invention, the oxide-modified,para-selective, zeolite-based catalyst composites as hereinbeforedescribed are treated with an organophosphorus reagent under particularconditions to enhance catalyst aromatics conversion para-selectivity,i.e., to either restore diminished para-selectivity or improve inherentpara-selectivity, or to reduce the susceptibility of the catalyst todeselectivation by contact with moisture. The organophosphorus reagentsutilized in the present invention are particular materials selected fromthe wide variety of phosphorus compounds which have heretofore been usedto modify aromatics conversion catalysts to enhance para-selectivity. Ithas now been suprisingly discovered that only certain of such phosphoruscompounds can be usefully employed in the context of the presentinvention to selectivate, reselectivate or reduce susceptibility tomoisture or halogen, e.g., chloride, deselectivation of the zeolitecatalysts herein whereas others of such phosphorus materials are noteffective in bringing about such para-selectivity-related improvements.

The particular organophosphorus reagents employed in the presentinvention are selected from C₁ to C₄ alkyl phosphite esters, C₁ to C₄alkyl phosphate esters and dimethylmethylphosphonate. The phosphite andphosphate esters include those having the formulas (R₁ O)(R₂ O)(R₃ O)Pand (R₁ O)(R₂ O)(R₃ O)P=O wherein R₁, R₂ and R₃ are each lower alkyl of1 to 4 carbon atoms. Examples of such organophosphous reagents includetrimethylphosphite, tributylphosphite, trimethylphosphate andtributylphosphate. Dimethylmethylphosphonate has the general formula CH₃P(O)(OCH₃)₂ and is the trimethyl derivative of phosphonic acid. Thepreferred organophosphorus reagents are trimethylphosphite anddimethylmethylphosphonate.

Catalyst contact with the organophosphorus reagent occurs with theorganophosphorus material in the vapor phase and under conditions whicheither enhance catalyst para-selectivity or reduce catalystdeselectivation susceptibility. Such conditions generally include acontact temperature of from about 100° C. to 300° C., more preferablyfrom about 150° C. to 300° C. Such conditions can also include anorganophosphorus reagent/catalyst contact time of from about 0.1 to 2hours, preferably from about 0.2 to 0.8 hours. The amount oforganophosphorus reagent employed is not critical so long as reagentcontact with the catalyst is sufficient to enhance the para-selectivityor reduce the deselectivation susceptibility of the treated catalystwith respect to its utility in promoting conversion of aromatics todialkyl substituted benzene compounds. Thus, generally catalyst can becontacted with at least about 0.5 gram of organophosphorus reagent pergram of catalyst per hour, more preferably with at least about 2 gramsof organophosphorus reagent per gram of catalyst per hour.

Organophosphorus reagent used to treat the specified catalysts of thepresent invention can be admixed with an inert inorganic gaseousdiluent. Inert diluent carriers of this type include nitrogen, carbondioxide, helium and the like. During contact with the modified catalyst,the organophosphorus treating agent mixture should be maintainedsubstantially free of organic diluents such as methanol.

After treatment with organophosphorus reagent, the modified catalysts ofthe present invention may optionally again be calcined in conventionalmanner to render the catalyst more suitable for use in promotingaromatics conversion reactions. Thus, after organophosphorus treatmentis completed to the extent desired, the treated modified catalyst can becontacted with an atmosphere maintained at a temperature from about 100°C. to 1000° C. for a period of from about 1 to 72 hours. Calcination isgenerally conducted in a suitable oxygen-containing atmosphere, e.g.air, which may also contain diluents such as nitrogen, helium and thelike.

It has been surprisingly discovered that treatment of the particularmodified zeolite catalyst composites of this invention withorganophosphorus reagent in the manner herein described can provide oneor more benefits with respect to catalyst para-selectivity when suchcatalysts are used to promote the conversion of aromatic compounds todialkyl substituted benzene compounds. In some instances, treatment ofoxide-modified zeolite catalysts with the particular organophosphorusmaterials described herein in accordance with the present invention willprovide enhancement of the para-selective characteristics of thecatalyst even though the catalyst may already be highly para-selectiveby virtue of the incorporation therein of the requisite difficultlyreducible oxide, for example, magnesium, calcium and/or even phosphorus.In other instances, treatment of the catalysts herein with theorganophosphorus materials of the present invention can bring aboutreselectivation of damaged para-selective catalysts which have had theirpara-selectivity characteristics diminished by contact with moisture orcontaminants such as metals or halogens in the course of hydrocarbonconversion operations. Finally, it has been discovered thatorganophosphorus treatment of either damaged or undamaged oxide-modifiedcatalysts in accordance with the present invention can reduce thesusceptibility of such catalysts to deselectivation by moisture orhalogen, e.g., chloride, contaminants, in the course of subsequentaromatics conversion operations.

The treated zeolite catalysts of the present invention areadvantageously used to promote conversion of aromatic compounds toprovide dialkyl substituted benzene product mixtures which are highlyenriched in the para-dialkyl substituted benzene isomer. Conversionreactions of this type thus include aromatics alkylation,transalkylation and disproportionation.

Alkylation of aromatic compounds in the presence of the above-describedcatalysts can be effected by contact of the aromatic with an alkylatingagent. A particularly preferred embodiment involves the alkylation oftoluene wherein the alkylating agents employed comprise methanol orother well known methylating agents or ethylene. The reaction is carriedout at a temperature of between about 250° C. and about 750° C.,preferably between about 300° C. and 650° C. At higher temperatures, thezeolites of high silica/alumina ratio are preferred. For example, ZSM-5having a SiO₂ /Al₂ O₃ ratio of 30 and upwards is exceptionally stable athigh temperatures. The reaction generally takes place at atmosphericpressure, but pressures within the approximate range of 10⁵ N/M² to 10⁷N/m² (1-100 atmospheres) may be employed.

Some non-limiting examples of suitable alkylating agents would includeolefins such as, for example, ethylene, propylene, butene, decene anddodecene, as well as formaldehyde, alkyl halides and alcohols, the alkylportion thereof having from 1 to 16 carbon atoms. Numerous otheraliphatic compounds having at least one reactive alkyl radical may beutilized as alkylating agents.

Aromatic compounds which may be selectively alkylated as describedherein would include any alkylatable aromatic hydrocarbon such as, forexample, benzene, ethylbenzene, toluene, dimethylbenzene,diethylbenzene, methylethylbenzene, propylbenzene, isopropylbenzene,isopropylmethylbenzene, or substantially any mono- or di-substitutedbenzenes which are alkylatable in the 4-position of the aromatic ring.

The molar ratio of alkylating agent to aromatic compound is generallybetween about 0.05 and about 2. For instance, when methanol is employedas the methylating agent and toluene is the aromatic, a suitable molarratio of methanol to toluene has been found to be approximately 0.1 to1.0 mole of methanol per mole of toluene. When ethylene is employed asthe alkylating agent and toluene is the aromatic, a suitable molar ratioof ethylene to toluene is approximately 0.05 to 2.5 moles of ethyleneper mole of toluene.

Alkylation is suitably accomplished utilizing a feed weight hourly spacevelocity (WHSV) of between about 1 and about 100, and preferably betweenabout 1 and about 50. The reaction product, consisting predominantly ofthe 1,4-dialkyl isomer, e.g. 1,4-dimethylbenzene,1-ethyl-4-methylbenzene, etc., or a mixture of the 1,4- and 1,3- isomerstogether with comparatively smaller amounts of 1,2-dialkylbenzeneisomer, may be separated by any suitable means. Such means may include,for example, passing the reaction product stream through a watercondenser and subsequently passing the organic phase through a column inwhich chromatographic separation of the aromatic isomers isaccomplished.

When transalkylation is to be accomplished, transalkylating agents arealkyl or polyalkyl aromatic hydrocarbons wherein alkyl may be composedof from 1 to about 5 carbon atoms, such as, for example, toluene,xylene, trimethylbenzene, triethylbenzene, dimethylethylbenzene,ethylbenzene, diethylbenzene, ethyltoluene, and so forth.

Another process embodiment of this invention relates to the selectivedisproportionation of alkylated aromatic compounds to producedialkylbenzenes wherein the yield of 1,4-dialkyl isomer is in excess ofthe normal equilibrium concentration. In this context, it should benoted that disproportionation is a special case of transalkylation inwhich the alkylatable hydrocarbon and the transalkylating agent are thesame compound, for example when toluene serves as the donor and acceptorof a transferred methyl group to produce benzene and xylene.

The transalkylation and disproportionation reactions are carried out bycontacting the reactants with the above described treated modifiedzeolite catalyst at a temperature of between about 250° C. and 750° C.at a pressure of between atmospheric (10⁵ N/m²) and about 100atmospheres (10⁷ N/m²). The reactant feed WHSV will normally fall withinthe range of about 0.1 to about 50. Preferred alkylated aromaticcompounds suitable for utilization in the disproportionation embodimentcomprise toluene, ethylbenzene, propylbenzene or substantially anymono-substituted alkylbenzene. These aromatic compounds are selectivelyconverted to, respectively, 1,4-dimethylbenzene, 1,4-diethylbenzene,1,4-dipropylbenzene, or other 1,4-dialkylbenzene, as appropriate, withbenzene being a primary side product in each instance. The product isrecovered from the reactor effluent by conventional means, such asdistillation, to remove the desired products of benzene anddialkylbenzene, and any unreacted aromatic component is recycled forfurther reaction.

The aromatics conversion processes described herein may be carried outas batch type, semi-continuous or continuous operations utilizing afixed or moving bed catalyst system. The catalyst after use in a movingbed reactor can be conducted to a regeneration zone wherein coke isburned from the catalyst in an oxygen-containing atmosphere, e.g. air,at an elevated temperature, after which the regenerated catalyst can berecycled to the conversion zone for further contact with the chargestock. In a fixed bed reactor, regeneration can be carried out in aconventional manner where an inert gas containing a small amount ofoxygen (0.5-2%) is used to burn the coke in a controlled manner so as tolimit the temperature to a maximum of around 500°-550° C.

The following examples will serve to illustrate certain specificembodiments of the hereindisclosed invention. These examples should not,however, be construed as limiting the scope of the invention, as thereare many variations which may be made thereon without departing from thespirit of the disclosed invention, as those of skill in the art willrecognize.

EXAMPLE I Preparation of Mg-P-ZSM-5 Alkylation Catalyst

A typical Mg-and P-modified catalyst composition illustrating one typeof catalyst used in evaluating the organophosphorus catalyst treatmentprocedure employed in this invention is described as follows. To preparesuch a catalyst, NH₄ ZSM-5 zeolite (9.75 kg.) having a crystal size ofabout 2 microns in the form of 1.6 mm (1/16 inch) diameter extrudatewith a 35 weight percent alumina binder is used. The catalyst ispresteamed at 593° C. for 2 hours at a gaseous steam rate of 2.83l./min. The catalyst material is then impregnated with a solution of 3.9kg. of diammonium acid phosphate in 16.2 l. of water and dried for about16 hours in an open dish. The catalyst is then calcined in air at 500°C. for 3 hours to give a phosphorus-modified zeolite. The resultingproduct is cooled, and a portion (1.36 kg.) is impregnated with asolution of 3.4 kg. of magnesium acetate tetrahydrate in 2.7 l. ofwater, dried and calcined in air at 500° C. for 1 hour. The finalcatalyst contains 7.1 weight percent magnesium, present at least in partas the oxide, and 2.67 weight percent phosphorus, present at least inpart as the oxide.

EXAMPLE II Ethylation of Toluene Over Mg-P-ZSM-5 Catalyst

An Mg-P-ZSM-5 zeolite catalyst prepared in a manner substantiallysimilar to that described in Example I is used to promote ethylation oftoluene. In such a reaction, WHSVs of 3.4 for toluene and 0.5 forethylene; a toluene to ethylene molar ratio of 2:1 and a temperature of400° C. are employed. The toluene conversion in such a reaction is 26.2%(Theoretical conversion =50%), with the concentration ofpara-ethyltoluene in the ethyltoluene product being 81.2%.

The Mg-P-ZSM-5 catalyst is then treated with trimethylphosphite (TMP) inaccordance with the method of the present invention. TMP along with anN₂ diluent is fed for 15 minutes into the catalyst at 250° C. The WHSVfor TMP is 3.1 and for the N₂ co-feed is 2.9. Before and after suchtreatment, the catalyst is calcined for one hour at 500° C.

After treatment with TMP in this manner, the catalyst is then used topromote ethylation of toluene under the same conditions employed withthe untreated catalyst. Toluene conversion using the TMP-treatedcatalyst is 19.7%. Selectivity to the para-ethyltoluene isomer is 100%.It can be seen from such experimentation that TMP treatment of thecatalyst improves the para-selectivity of the Mg-P-ZSM-5 catalyst eventhough the catalyst has already been phosphorus-modified in conventionalmanner with diammonium acid phosphate.

EXAMPLE III Preparation of Mg-ZSM-5 Alkylation Catalyst

A sample of NH₄ ZSM-5 having a crystallite size of approximately 2microns, containing 35 percent alumina binder, in the form of 1.6 mm(1/16 inch) extrudate is treated for 1 hour with a 60 wt % solution ofMg(NO₃)₂.6H₂ O in water. Thereafter the catalyst is filtered, dried andcalcined in air to provide a catalyst composite which containsapproximately 5% by weight of magnesium. Catalysts of this general type,in some cases damaged by exposure to water or contaminants, are used insubsequent exemplification herein to demonstrate the catalyst treatmentprocess of the present invention.

EXAMPLE IV Para-Selective Aromatics Conversion Over Damaged Mg-ZSM-5

A procedure was established to evaluate various test catalysts of theExample III type for their performance in promoting para-selectivearomatic conversion reactions. In accordance with such a procedure, 2.2grams of the test catalyst, 14-24 mesh, is centered in a quartz reactor.Low surface area quartz chips are used to position the catalyst and fillvoid spaces. After calcination with air at 500° C. for one hour, thetemperature is adjusted to 425° C. Toluene is fed to the reactor at arate of 8.8 cc/hr. with a WHSV of 3.5. A temperature rise occurs, andtemperature is immediately adjusted to 450° C. After 25 minutes onstream at 450° C., a water condenser is used to collect the liquidproduct for a period of 5 minutes for analysis. A 2 cc gas sample isalso taken at this time for analysis at a position just after the watercondenser. The temperature is then increased rapidly and successively to500° C., 550° C. and 600° C. In a similar manner, liquid and gaseoussamples are taken for analysis at each temperature during the last fiveminutes of a 30-minute run. This series of tests is used to determineperformance for selective toluene disproportionation to produce p-xyleneand benzene.

The reactor is then purged with nitrogen (without regeneration) and thetemperature adjusted to 375° C. Toluene is fed at a rate of 19.8 cc/hr,WHSV of 7.8, then ethylene is added at 15.6 cc/min., WHSV of 0.5, andthe nitrogen purge is stopped. The temperature is rapidly adjusted to400° C. In a similar manner, gaseous and liquid samples are taken duringthe last five minutes of a 30-minute run. An additional test run is madeat 450° C. This series of tests is used to determine performance for thealkylation of toluene with ethylene to produce p-ethyltoluene.

The reactor is purged with nitrogen, and the temperature adjusted to380° C. without regeneration. A 4/1 molar mixture of toluene/methanol ata rate of 29 cc/hr., WHSV=11, is fed to the reactor and the temperatureimmediately adjusted to 400° C. In a similar manner; samples of gas andliquid are taken during the last five minutes of each 30-minute run at400° C., 500° C. and 600° C.

Using these catalyst evaluation procedures, a sample of a base catalystas generally described in Example III was tested for its performance inthe toluene disproportionation and alkylation reactions described. Sucha catalyst had been previously employed in a pilot plant operation topromote ethylation of toluene and had been damaged by exposure tomoisture in the toluene feed. Results are provided in Table I.

                  TABLE I                                                         ______________________________________                                        Para-Selectivity of Damaged Mg--ZSM-5 Base Catalyst                                       SELECTIVITY TO   CONVERSION                                                   PARAISOMER       RANGE                                            REACTION    (% by weight)    (% by weight)                                    ______________________________________                                        Toluene                      1.2-17.3                                         Disproportionation                                                            450° C.                                                                            67.8                                                              500° C.                                                                            65.4                                                              550° C.                                                                            58.4                                                              600° C.                                                                            52.6                                                              Toluene Alkylation           9.3-13.9                                         w/Ethylene                                                                    400° C.                                                                            88.3                                                              450° C.                                                                            84.5                                                              Toluene Alkylation           8.7-17.3                                         w/Methanol                                                                    400° C.                                                                            87.1                                                              500° C.                                                                            73.5                                                              600° C.                                                                            64.5                                                              ______________________________________                                    

The Table I data illustrate that the damaged Mg-ZSM-5 catalyst samplestill exhibits some para-selectivity which, unlike conversion, decreaseswith increase in temperature.

EXAMPLE V Para-Selective Aromatics Conversion overOrganophosphorus-Treated Mg-ZSM-5

Samples of the damaged Mg-ZSM-5 catalyst of Example IV are treated withvarious organophosphorus reagents under various temperature conditionsand then again tested for aromatics conversion activity and selectivityin accordance with the procedures of Example IV. In such testing, thedamaged Mg-ZSM-5 which had been used in the base aromatics conversiontesting of Example IV is calcined at 500° C. for one hour and thensubjected to the organophosphorus treating agent for 15 minutes at thedesired treatment temperature. Organophosphorus reagent is passed overthe catalyst bed at the rate of 15 ml/hr; nitrogen is co-fed at a rateof approximately 60 cc/min. Following treatment, the catalyst sample isagain calcined at 500° C. for one hour and then used in the aromaticsconversion testing procedure hereinbefore described.

Results of such aromatics conversion testing for catalyst samplestreated with trimethylphosphite [P(OCH₃)₃ ], tributylphosphite [P(OC₄H₉)₃ ], tributylphosphine [P(C₄ H₉)₃ ]and tributylphosphonate [(C₄ H₉O)₂ (C₄ H₉)P=O] are shown in Table II.

                                      TABLE II                                    __________________________________________________________________________    TREATED DAMAGED Mg--ZSM--5                                                    (Para-Isomer in Primary Product, %, and Toluene Conversion, %)                            TMP, TMP,  P(OBu).sub.3,                                                                      P(OBu).sub.3,                                                 200° C.                                                                     500° C.                                                                      100° C.                                                                     300° C.                                                                      PBu.sub.3                                                                          PBu.sub.3                                                                           (BuO).sub.2 BuP═                                                                   (BuO).sub.2                                                                   BuP═ O,                         15 min.sup.(a)                                                                     15 min                                                                              15 min                                                                             15 min                                                                              100° C.                                                                     300° C.                                                                      100° C.                                                                         500°             __________________________________________________________________________                                                          C.                      TOL DISPROPORT.sup.(b)                                                           450° C.                                                                         88.9 70.4  72.1 92.7  70.8 63.9  65.6     41.8                    500         92.5 69.4  71.1 93.8  65.9 56.8  60.4     40.6                    550         93.5 64.4  67.8 92.4  60.7 53.7  58.4     44.1                    600         92.0 73.9  63.4 91.1  56.2 49.9  55.6     47.3                    (Conv)      0.9-7.0                                                                            0.7-1.6                                                                             1.5-15.5                                                                            1.0-11.3                                                                           1.1-16.1                                                                           1.7-18.5                                                                             1.5-17.9                                                                              1.7-4.1                 TOL + C.sub.2 H.sub.4.sup.(c)                                                    400° C.                                                                         98.8 100   91.2 98.4  88.6 85.2  88.7     75.1                    450         98.5 100   89.0 98.1  85.9 81.8  86.9     74.4                    (Conv)      6.9-8.9                                                                            0.8-0.9                                                                             7.7-9.9                                                                            6.2-7.5                                                                             7.0-10.1                                                                           7.4-11.0                                                                            6.6-9.4   1.9                    TOL + MeOH.sup.(d)                                                               400° C.                                                                         97.9 55.1  90.9 94.5  88.9 88.2  54.0     64.4                    500         97.2 65.3  85.3 90.9  80.6 81.3  50.1     59.2                    600         92.6 72.1  65.1 60.2  69.4 70.7  62.8     57.5                    (Conv)       6.3-10.4                                                                           7.0-17.0                                                                           9.3-19.5                                                                           1.9-6.6                                                                             10.7-20.2                                                                          10.0-20.0                                                                           0.6-1.0  1.5-2.0                 __________________________________________________________________________     .sup.(a) Reagent and catalyst treatment conditions.                           .sup.(b) Selective toluene disproportionation.                                .sup.(c) Alkylation of toluene with ethylene to produce pethyltoluene.        .sup.(d) Alkylation of toluene with methanol to product pxylene.         

A comparison of the aromatics conversion data from Tables I and IIindicates that the trialkylphosphite treating agents of the presentinvention can, within the temperature ranges of the present invention,restore para-selectivity to the damaged Mg-ZSM-5 catalyst without undueloss of catalyst activity. Similar organophosphorus treating agents notwithin the scope of the present invention either do not significantlyrestore lost catalyst para-selectivity or do so at a significant loss ofcatalyst activity.

EXAMPLE VI

In this example, an Mg-ZSM-5 catalyst having para-selectivity diminishedby generation of water during catalyst contact with methanol is treatedseveral times with trimethylphosphite (TMP) and tested for its aromaticsconversion performance in accordance with the general procedures ofExample IV. In such TMP treatments, the catalyst sample is calcined at500° C. for 1 hour and is then cooled to 155° C. TMP is metered into thecatalyst bed at the rate of 20 ml/hr and mixed with nitrogen flowing ata rate of 100 cc/min. An exothermic reaction occurs to increase thetemperature to about 190° C. in six minutes. The temperature isincreased to 200° C. and maintained for about 15 minutes. The TMP feedis terminated, nitrogen flow is continued for about 5 minutes, and thenair is introduced slowly as the temperature is increased to 550° C. overa period of about 30 minutes and maintained for a period of two hours ina flow of air at 100 cc/min.

A summary of the catalyst treatment procedures and the aromaticconversion screening results is provided in Table III.

                                      TABLE III                                   __________________________________________________________________________     Treatment of Mg--ZSM--5 Damaged by Water Generated During Methanol           Conversion                                                                    __________________________________________________________________________    CATALYST Mg--ZSM--5 P--Mg--ZSM--5                                                                           P--Mg--ZSM--5                                                                           P--P--ZSM--5                                                                            P--P--P--Mg--ZSM--5                             Gaseous TMP,                                                                  Runs 1-9  Calcine, 1 Hr                                                                           Gaseous TMP                                                                             Gaseous TMP                                     *Pure MeOH Used                                                                         500° C., Air                                                                     2nd Impreg.                                                                             3rd Impreg.                 TREATMENT                                                                              None       Runs 10-12                                                                              Runs 13-18                                                                              Runs 19-24                                                                              Runs 25-30                           Conv %                                                                              Para %                                                                             Conv %                                                                             Para %                                                                             Conv %                                                                             Para %                                                                             Conv %                                                                             Para %                                                                             Conv % Para %               TOLUENE                                                                       DISPROPORT.                                                                      400° C.                                                                      1.2   95.8 1.6  94.3 0.9  78.9 0.6  86.0 0.5    86.7                 450      3.3   95.6 3.0  96.8 1.9  76.7 1.0  88.3 0.7    87.3                 500      7.7   95.0 5.0  96.8 4.5  73.5 2.1  89.0 1.2    89.9                 550      13.4  94.2 7.9  95.5 9.1  69.9 4.3  88.0 2.1    91.8                 TOL + C.sub.2 H.sub.4                                                            400° C.                                                                      8.0   100  6.9  100  13.3 90.5 10.9 97.3 7.0    100                  450      6.8   100  4.7  100  10.6 86.8 9.5  96.3 6.3    100                  TOL + MeOH                                                                       400° C.                                                                      6.4   98.4 2.2  68.3                                                 500      9.3   96.2 4.3  87.5                                                 600      8.5   94.5 5.6  65.1                                                 __________________________________________________________________________     *Results of Runs 10-12 wherein catalyst is contacted with pure methanol       are not shown. Reaction of catalyst with methanol generates water in the      catalyst bed which reduces catalyst selectivity. In subsequent runs, the      methanol feed is not used and toluene methylation is not tested.         

As the Table III data indicate, the initial screening shows highpara-selectivity in all three types of toluene conversion for thecatalyst sample. The initial treatment with TMP did not significantlyincrease para-selectivity for toluene disproportionation and ethylationsince catalyst para-selectivity was already high initially. Whenmethanol feed is used, water is generated in the catalyst bed andsignificantly reduces para-selectivity for all types of subsequenttoluene conversion. Table III further indicates that this loss ofcatalyst para-selectivity is not restored by calcination alone, but thatsubsequent treatments with TMP can restore such diminishedpara-selectivity for the toluene disproportionation and ethylationreactions.

EXAMPLE VII Treatment of Mg-ZSM-5 Damaged by Contamination with Metalsand Halogen

An alkylation unit using Example III type Mg-ZSM-5 with two catalystbeds connected in series is used to test catalyst performance foralkylation of toluene with ethylene to produce p-ethyltoluene (PET).Half of the ethylene feed is mixed with the toluene feed leading to thefirst reactor. The other half is added to the effluent from the firstreaction prior to passage through the second bed. Selectivity to PETdeclined with time. An analysis of the catalyst revealed contaminationwith metals and chloride as follows:

    ______________________________________                                        Analysis of Damaged PET Alkylation Catalyst                                             Analysis, wt. %                                                     Reactor     Mg     Cl         Fe   Ni                                         ______________________________________                                        Top         8.61   0.89       0.34 0.02                                       Bottom      8.49   0.93       0.35 0.02                                       ______________________________________                                    

Subsequent investigation revealed that the toluene feed was contaminatedwith chlorinated hydrocarbons.

This contaminated catalyst was treated with gaseous trimethylphosphitein the manner described in Example VI. Catalyst was again tested fortoluene disproportionation and ethylation in accordance with theprocedures described in Example IV. Results are summarized in Table IV.

                  TABLE IV                                                        ______________________________________                                        Treatment of Damaged Mg--ZSM-5 with TMP                                                       After        After                                            New             Damage in    Treatment                                        Catalyst        Reactor      with TMP                                         Conv.       Para    Conv.    Para  Conv. Para                                 %           %       %        %     %     %                                    ______________________________________                                        A. TOL                                                                        DISPRO.                                                                       450° C.                                                                        1.2     95.8    1.2    72.6  0.9   89.8                               500     3.3     95.6    3.0    70.7  1.9   91.6                               550     7.7     95.0    7.9    69.3  4.3   91.1                               600     13.4    94.2    14.5   64.6  9.0   89.3                               B. TOL +                                                                      C.sub.2 H.sub.4                                                               400° C.                                                                        8.0     100     12.9   94.8  10.5  99.1                               450     6.8     100     10.2   92.6  8.9   98.8                               ______________________________________                                    

The Table IV data demonstrate that trimethylphosphite can be used toreselectivate ZSM-5 type catalysts which have been damaged by metal andhalogen contamination.

EXAMPLE VIII Susceptibility of Organophosphorus Treated Mg-ZSM-5 toMoisture Damage

An Mg-ZSM-5 catalyst of the type prepared in Example III is tested forits conversion and para-selectivity for promotion of ethylation oftoluene. The catalyst is then intentionally damaged by introduction ofmoisture and again tested in toluene ethylation reactions. The catalystsample is then treated with gaseous trimethylphosphite or gaseoustrimethylphosphate and again tested for its activity andpara-selectivity in promoting ethylation of toluene. Organophosphorustreated catalyst is then again subjected to moisture treatment and againtested for its toluene ethylation performance. In this manner, theeffect of organophosphorus treatment on catalyst moisture susceptibilityis demonstrated.

Reaction conditions and conversion and selectivity performance for thistesting is set forth in Tables V and VI.

                  TABLE V                                                         ______________________________________                                        Use of TMP.sup.1 to Regenerate Damaged Alkylation Catalyst.sup.2              And to Reduce Susceptibility to Moisture                                      Conditions % Toluene Conversion.sup.3                                                                    % Para Selectivity                                 ______________________________________                                        .sup.4 Toluene + C.sub.2 H.sub.4                                                         23.5            96.1                                               .sup.5 H.sub.2 O treatment                                                               26.9            88.4                                               Toluene + C.sub.2 H.sub.4                                                     .sup.6 TMP treatment                                                                     27.4            99.2                                               Toluene + C.sub.2 H.sub.4                                                     H.sub.2 O Treatment                                                                      24.0            98.7                                               Toluene + C.sub.2 H.sub.4                                                     ______________________________________                                         .sup.1 Trimethylphosphite, (CH.sub.3 O).sub.3 P                               .sup.2 Mg--ZSM5                                                               .sup.3 Theoretical conversion = 50%                                           .sup.4 Toluene = 3.4 WHSV, C.sub.2 H.sub.4 = 0.5 WHSV; Tol: C.sub.2           H.sub.4 = 2:1; T = 400° C.                                             .sup.5 H.sub.2 O = 6.0 WHSV, N.sub.2 cofeed = 2.9 WHSV at 400° C.      for 30 min. 30 min N.sub.2 purge at 400° C. before and after           treatment.                                                                    .sup.6 TMP = 3.1 WHSV, N.sub.2 cofeed =  2.9 WHSV at 250° C. for 1     min. 1 hour calcination at 500° C. before and after treatment.    

                  TABLE VI                                                        ______________________________________                                        Use of TMPO.sup.1 to Regenerate Damaged Alkylation Catalyst.sup.2             And to Reduce Susceptibility to Moisture                                      Conditions % Toluene Conversion.sup.3                                                                    % Para Selectivity                                 ______________________________________                                        .sup.4 Toluene + C.sub.2 H.sub.4                                                         26.6            96.3                                               .sup.5 H.sub.2 O treatment                                                               27.3            80.8                                               Toluene + C.sub.2 H.sub.4                                                     .sup.6 TMPO treatment                                                                    29.2            96.3                                               Toluene + C.sub.2 H.sub.4                                                     H.sub.2 O Treatment                                                                      26.2            95.7                                               Toluene + C.sub.2 H.sub.4                                                     ______________________________________                                         .sup.1 Trimethylphosphate, (CH.sub.3 O).sub.3 P = O                           .sup.2 Mg--ZSM5                                                               .sup.3 Theoretical conversion = 50%                                           .sup.4 Toluene = 3.4 WHSV, C.sub.2 H.sub.4 = 0.5 WHSV; Tol: C.sub.2           H.sub.4 = 2:1; T = 400° C.                                             .sup.5 H.sub.2 O = 6.0 WHSV, N.sub.2 cofeed = 2.9 WHSV at 400° C.      for 30 min. 30 min N.sub.2 purge at 400° C. before and after           treatment.                                                                    .sup.6 TMPO = 3.1 WHSV, N.sub.2 cofeed = 2.9 WHSV at 250° C. for 1     min. 1 hour calcination at 500° C. before and after treatment.    

The ability of both gaseous trimethylphosphite and gaseoustrimethylphosphate to reselectivate damaged Mg-ZSM-5 alkylationcatalysts is demonstrated by the Table V and VI data. Both samples ofthe catalyst were subjected to the same moisture damaging conditions.The reason for one sample suffering a greater loss in para-selectivity(80.8% vs. 88.8/4%) is unknown. The sample treated with TMP wasreselectivated to a para-selectivity (99.2%) greater than that exhibitedby the undamaged catalyst (96.1%). In addition, there was a slightimprovement in toluene conversion (27.4% for reselectivated catalyst vs23.5% for undamaged catalyst). Treatment with TMPO restored the damaged(80.8% para-selectivity) catalyst to its pre-damaged para-selectivity of96.3%. Although para-selectivity shows a greater improvement after TMPtreatment that after TMPO treatment, this may be a result of the factthat the sample used for TMP treatment had not sustained as much damageas the sample used in the TMPO study. Both reselectivated catalystsamples exhibited remarkable resistance to moisture following thetreatment. When both catalyst were subjected to a second watertreatment, little decrease in para-selectivity was observed.Para-selectivity for the TMP treated catalyst decreased from 99.2%before the second water treatment to 98.7% after the treatment.Para-selectivity for the TMPO treated catalyst decreased from 96.3% to95.7% after the second water treatment.

EXAMPLE IX

An Mg-ZSM-5 catalyst of the type prepared in Example III is tested forits propensity to adsorb selectivity-damaging chloride from achloride-contaminated toluene feed during a toluene alkylation reaction.Such a toluene alkylation reaction is run for 24 hours on stream usingtoluene containing 25 ppm Cl (Toluene WHSV=4.7) and an ethylenealkylating agent (Ethylene WHSV=0.4) at a temperature of 400° C.Chloride adsorption by the untreated catalyst, both before and aftercalcination for 1 hour at 500° C., during such a reaction is determined.The same catalyst is then tested in a similar manner after the catalysthas been treated with two different organophosphorus reagents,trimethylphosphite (TMP) and dimethylmethylphosphonate (DMMP). Treatmentconditions, chloride adsorption results, and catalyst phosphorus contentare set forth in Table VII. Chloride adsorption percentages in Table VIIrepresent an average of three determinations.

                  TABLE VII                                                       ______________________________________                                        Relative Chloride Adsorption by Untreated and Organophos-                     phorus-Treated Mg--ZSM-5 Toluene Alkylation Catalyst                                         % Cl                                                                                Before     After                                         Catalyst Treating Agent                                                                            Calcination                                                                              Calcination                                                                           % P                                   ______________________________________                                        Mg--ZSM-5                                                                              None        0.62       0.34    0.01                                  Mg--ZSM-5                                                                              TMP.sup.1   0.02       0.02    1.00                                  Mg--ZSM-5                                                                              DMMP.sup.2  0.02       0.02    1.00                                  ______________________________________                                         .sup.1 TMP = 15 ml/hr with N.sub.2 CoFeed at 100 cc per minute  Treatment     time is 15 minutes at 200° C.                                          .sup.2 DMMP = 4.3 ml/hr with N.sub.2 CoFeed at 200 cc per minute              Treatment time is 30 minutes at 150° C.                           

The Table VII data demonstrate that catalyst treatment with either TMPor DMMP can significantly reduce the tendency of an Mg-ZSM-5 alkylationcatalyst to adsorb selectivity-damaging chloride fromchloride-contaminated toluene during a toluene alkylation reaction.

What is claimed is:
 1. A process for conversion of aromatic compounds to a dialkyl benzene compound mixture enriched in the paradialkylbenzene isomer, said process comprising contacting said aromatic compounds with an alkylating agent under conversion conditions with a catalyst comprising both a crystalline zeolite material having a constraint index within the approximate range of 1 to 12 and a silica/alumina mole ratio of at least 12 and a minor proportion of one or more difficultly reducible oxides, said catalyst being prepared by a method comprising contacting said catalyst with a vapor phase organophosphorus reagent selected from C₁₋₄ alkyl phosphite esters, C₁₋₄ alkyl phosphate esters and dimethylmethylphosphonate, at a temperature of 100° C. to 300 ° C. and for a period of time and under conditions sufficient to either enhance para-selectivity of said catalyst or to reduce the susceptibility of said catalyst to deselectivation by contact with moisture or halogen.
 2. A process according to claim 1 wherein said aromatic compounds comprise toluene and said alkylating agent contains from 1 to about 16 carbon atoms and is selected from olefins and alkyl halides.
 3. A process according to claim 1 wherein said difficultly reducible oxide is selected from magnesium oxide, calcium oxide, phosphorus oxide, combinations of magnesium oxide and phosphorus oxide and combinations of calcium oxide and phosphorus oxide.
 4. A process according to claim 1 wherein contact between catalyst and organophosphorus reagent occurs at a temperature of from about 150° C. to 250° C., wherein organophosphorus reagent is contacted with catalyst for a period of from about 0.2 to 1.0 hour; and wherein catalyst is contacted with at least about 0.5 gram of organophosphorus reagent per gram of catalyst per hour.
 5. A process according to claim 1 wherein said catalyst is contacted with organophosphorus reagent admixed with an inert gaseous diluent selected from nitrogen, carbon dioxide and helium.
 6. A process according to claim 1 wherein said zeolite is selected from ZSM-5, ZSM-11, ZSM-12,ZSM-23, ZSM-35, ZSM-38 and ZSM-48.
 7. A process according to claim 1 wherein the organophosphorus reagent is trimethylphosphite, tributylphosphite, trimethylphosphate, tributylphosphate, or dimethylmethylphosphonate.
 8. A process according to claim 1 wherein said catalyst comprises from about 1 to 99% by weight of zeolite material with the balance of said composition comprising a binder for said zeolite material. 